Relatively hard materials are often processed for mining and construction. The variety of materials include rock, concrete, asphalt, coal, and a variety of other types of mineral-based materials. A number of different methods for reducing the size of these hard materials have been developed. One traditional material size reduction method has been to drill relatively small holes in the material which are then packed with an explosive that is ignited, resulting in a rapid and cost effective method of size reduction. However, there are a variety of disadvantages to this technique, including the inherent risk of injuries, the production of undesirable noise, vibrations, and dust, and the fact that this process is difficult to utilize in situations where space is limited or where there is a potential risk of causing other gases to ignite.
Due to the above-described disadvantages associated with blasting techniques, alternative methods have been developed for reducing large surface areas of relatively hard materials. One alternative has been the use of reducing machines having rotary reducing components that move rigid and specialized reducing elements through paths of travel. The reducing components can include rotating cutting drums that move the reducing elements through circular paths of travel. Such drums are typically attached to corresponding machines with a mechanism that allows the position and orientation of the drum to be controlled, so as to bring the reducing elements into contact with the material being reduced.
An example machine of the type described above is disclosed in U.S. Pat. No. 7,290,360. The disclosed machine is a surface excavation machine used for applications such as surface mining, demolishing roads, terrain leveling, and prepping sites for new construction or reconstruction by removing one or more layers of material. Surface excavation machines of this type provide an economical alternative to blasting and hammering and provide the advantage of generating a consistent output material after a single pass.
On some rotating cutting drums, certain cutting patterns, created by particular arrangements of the reducing elements along the surface of the drum, are used to achieve different cutting results. This is done for a variety of reasons, for instance to counter dust production and to achieve smoother cutting operation of the rotating cutting drum. See U.S. Patent Pub. No. 2006/0255649 and U.S. Pat. No. 4,119,350.